An electronic device such as a car-navigation system and a portable personal computer has a clock function for performing various kinds of controls based on time information obtained by the clock function. For example, functions such as time display and estimation of arrival time to a destination in a car-navigation system and time stamp of a file generated in a personal computer are performed based on the time information.
The standard time of each area of a country in the world is determined to have time difference of a multiple number of 1 hour or 30 minutes from the Coordinated Universal Time (UTC: Universal Time Coordinated). For example, Japan is assigned the Japanese standard time (JST: Japan Standard Time), which has time difference from the Coordinated Universal Time and is advanced from the Coordinated Universal Time by 9 hours. Therefore, the Japanese standard time is noted by “+0900 (JST)” or “UTC+9.” The standard time is assigned to each predetermined region as a time zone substantially divided in the longitudinal direction in consideration of the rotation axis of the earth. The United States excluding Alaska is divided into four time zones, which are assigned to continuing land. When a person moves from New York (UTC-5) to San Francisco (UTC-8), the person passes through two time zones. New York (UTC-5) and San Francisco (UTC-8) therebetween have time difference of 3 hours.
For example, JP-A-9-297191 discloses an automatic correction device configured to calculate time difference between one time zone and another time zone when moving from the one time zone to the other time zone. The automatic correction device is further configured to automatically correct and change displayed time based on the calculated time difference. In JP-A-9-297191, the automatic correction device detects a self-position based on positioning information obtained using a global positioning system (GPS), determines the time zone where the self position is, and automatically corrects the displayed time based on the time difference information of the time zone. It is conceived to apply the automatic correction device disclosed in JP-A-9-297191 to a system such as a car-navigation system configured to frequently detect the self-position. However, in this case, the displayed time may be frequently changed and corrected whenever the time zone where the self-position changes. Specifically, in a case where a vehicle runs on a road to go beyond a boundary of time zones frequently, for example, the displayed time is frequently changed and corrected. In this case, a user may feel uncomfortable due to frequent correction of the displayed time.